A CVT is to control continously speed ratio e (=output side rotational speed Nout/input side rotational speed Nin) to be used for a vehicle as a power transmission system having excellent specific fuel consumption. In the CVT, a desired engine speed No is set as a function of running parameter of an engine such as intake throttle position .theta., vehicle speed V or the like and the CVT is controlled such that an actual engine speed Ne becomes the desired engine speed No. However, to provide drive feeling and drivability corresponding to the excellent specific fuel consumption and vehicle speed, the desired engine speed was set to a low value in low vehicle speed according to Pat. No. Sho-58-17551 applied previously by this applicant. Thus, even if a driver tries to accelerate a vehicle from a low vehicle speed in climbing a extremely steep slope by pedalling an accelerator pedal, the engine speed Ne is just slightly increased and engine output is not so much increased that unsatisfactory acceleration is disadvantageously provided.